This application is based on Japanese Patent Application Nos. 11-227942 (1999) filed Aug. 11, 1999, and 2000-217757 (2000) filed Jul. 18, 2000, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an image printing apparatus for printing various kinds of image information in personal computers, word processors, electronic typewriters, facsimiles or the like.
2. Description of the Prior Art
Recently, office automation equipment, such as personal computers and word processors, has come to be used widely in individual households. It is becoming commonplace for the users of this kind of equipment to upload photoprints, process and output images or the like by using input means such as a digital camera and a film scanner.
Under such circumstances, the image printing apparatus, as one of the various output means, is increasingly required to be provided with the ability to output a high-quality image such as the photoprint, and it has been improved in various aspects in order to meet such requirement. At present, a so-called serial-type image printing apparatus designed for obtaining a desired print by scanning a printing medium with a printing head is prevailing mainly due to the printing cost. A means for improving the quality of the image obtainable by the serial-type image printing apparatus is to improve the positioning accuracy of the printing head relative to the printing medium.
In a serial-type image printing apparatus, the printing head is attached to a carriage, and the carriage is moved, for scanning, in a breadthwise direction of the printing medium by a stepping motor. The printing head is driven correspondingly to the timing of the driving operation of the stepping motor to effect the printing operation of the printing head to the printing medium. Is this case, in order to scan the carriage at a constant speed, it is necessary for the stepping motor to be driven with a constant revolution. The amount of revolution of the stepping motor and the scanning movement of the carriage do not necessarily have a one-to-one relationship because of structural factors such as the delay of the rotor relative to the excitation phase of the stepping motor or the vibration of the cogged belt for coupling the stepping motor and the carriage. In other words, driving the printing head correspondingly to the driving revolution of the stepping motor does not necessarily assure the formation of good images.
Therefore, in order to resolve the problem of a decrease in imaging quality caused by the previously mentioned structural factors, it is necessary to detect the absolute position of the carriage, on which the printing head is attached, so that the printing head can be driven correspondingly to the detection signal.
As for the method for detecting the absolute position of the carriage, it is a common practice to read, by means of an optical or magnetic sensor mounted on the carriage, the position of the carriage on the basis of the linear encoder scale, which covers the full stroke of the carriage.
FIG. 12 shows a schematic illustration of the carriage in a conventional image printing apparatus. In this illustration, a guide shaft 104, for defining the direction of scanning movement of the carriage 102, slidably passes through a guide bush 103, which is provided at the rear end of the carriage 102, whereon a printing head 101 is attached for forming image on a printing medium (not shown). The carriage 102 is made to move for scanning along the guide shaft 104 when the cogged belt (not shown), connected with the carriage 102, is driven. The linear encoder scale 105 provided in parallel with the guide shaft 104, consists of a transparent PET (polyethylene terephthalate) web with black scale printed thereon at predetermined intervals. A printed circuit board 106 mounted at the rear end of the carriage 102 is provided not only with various devices, such as a capacitor 107, for driving the printing head 101 but also with an optical encoder sensor 108 for detecting the position of the carriage 102 by optically reading the scale on the linear encoder scale 105.
The position of the carriage 102 with respect to the linear encoder scale 105 can be determined accurately by reading the scale printed on the linear encoder scale 105 by using the encoder sensor 108 while the carriage 102 is moving for scanning. Any desired image can be printed on the printing medium by driving the printing head 101 correspondingly to the detection signal.
In the case of the conventional image printing apparatus illustrated in FIG. 12, the paper dust produced by the friction occurring during the transfer of the printing medium or the common dust, occurring depending on its location, accumulates on the linear encoder scale 105 and the encoder sensor 108. Especially, in the case of the ink-jet printer, the ink and the treatment liquid for adjusting the printability of the ink to the printing medium, which are discharged from the printing head, form floating mist to accumulate on the linear encoder scale 105 and the encoder sensor 108. As a result, during the long use of the image printing apparatus, foreign matters such as previously mentioned paper dust, common dust or the mist adheres to the linear encoder scale 105, thereby not only making the linear encoder scale 105 hard to be read accurately but also making it difficult to print high-quality image on the printing medium.
When using a magnetic-type encoder as the linear encoder scale 105, the adhesion of foreign matters such as the paper dust, common dust and mist can be prevented by closely attaching a cover to the linear encoder scale. This type of image printing apparatus is disclosed in Japanese Patent Application Laid-open No. 5-298628 (1993) and U.S. Pat. No. 5,450,106. However, when an optical-type encoder is adopted, if the cover is closely provided with the linear encoder scale, there is the possibility that the linear encoder scale is damaged or contaminated widely by the paper dust, common dust or the mist. And, this can adversely affect the accurate reading by the encoder sensor.
The object of the present invention is to provide an image printing apparatus capable of printing high-quality images on the printing medium over a long period of time not only by preventing the foreign matters such as the paper dust, common dust or the mist from adhering to the scale or the sensor but also by preventing the linear encoder scale from being damaged.
An image printing apparatus according to the present invention includes means for conveying a printing medium and means for scanning a carriage to move across the direction in which the printing medium is conveyed by the printing medium conveying means, the carriage being attached to a printing head for printing an image on the printing medium, the image printing apparatus comprising:
a scale disposed along the direction of scanning of the carriage by the scanning means,
a sensor for detecting the position of the carriage relative to the scale, the sensor being mounted on the carriage opposite to the scale, and
a cover for covering the sensor and at least a part of the scale adjoining the sensor, the cover being provided with a guide portion for guiding the scale to a predetermined position with respect to the sensor.
According to the present invention, because the image printing apparatus comprises the cover for covering the sensor which is provided with the carriage so that the sensor opposes the scale disposed along the direction of scanning of the carriage, with the cover being provided with a guide portion for guiding the scale to a predetermined position with respect to the sensor, foreign matters such as the paper dust, common dust or the like adheres only on the surface of the cover, preventing them from adhering to the sensor and the scale. The scale is guided to a predetermined position relative to the sensor by the guide portion of the cover to enable accurate reading of the scale, and as a result, reliable and high-quality printing of images can be obtained by the image printing apparatus over a long period of time.
In the image printing apparatus according to the present invention, the cover may be mounted on the carriage, the cover also may be disposed for covering the full length of the carriage. In the case the cover is provided to cover the full length of the carriage, the cover preferably includes a slit for permitting the sensors to pass through. At least a part of the cover may be formed from an elastic material or conductive material. In case the cover is formed from a conductive material, the adhering of the dust to the cover due to the effect of the static electric charge can be inhibited.
In the case the guide portion of the cover is provided so as to prevent the sensor from coming into contact with the scale, the scale can be protected from being scratched as the result of the contact between the scale and the sensor or the foreign matter.
The guide portion is preferably designed so as to be able to prevent the contact between the sensor and the scale even during the movement of the carriage for scanning. Further, the guide portion is preferably opposed to the scale so that the part of the scale corresponding to the reading center of the sensor is interposed with respect to the guide portion.
The area of the central portion of the cover may be made larger than that of the opening end of the cover through which the scale passes. In this case, the incursion of the foreign matter into inside of the cover can be prevented more effectively for better protection of the sensor and the scale.
An absorption member may be received within the cover. Thereby, this absorbing member catches the foreign matter invading within the cover to prevent them more effectively from adhering to the sensor or the scale.
The image printing apparatus may also comprise opening/closing means for opening/closing the opening end of the cover through which the scale passes. In case the opening/closing means is provided, the dust and the like can be prevented from entering within the cover while the image printing apparatus is not operating, thereby preventing the dust and the like from adhering to the sensor and the scale. In this case, means for controlling the opening/closing means so that the opening end of the cover can be closed during the operation of the carriage scanning means is not activated.
The printing head may be a liquid ejecting head having an ejecting port for ejecting liquid. In this case, the liquid ejecting head may include an ejecting energy generator for generating the energy to eject liquid from the ejecting port. The ejecting energy generator may include an electrothermal transducer for generating thermal energy through the film boiling of the liquid. The liquid may be ink and/or a treating liquid for adjusting the printability of the ink to be ejected onto the printing medium.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.